Field of the Invention
The present invention relates to a means and a method for detecting a capacitive type touch input of a touch input means like a finger of a human body or a touch input means having a conductive property similar thereto, and more particularly, to a capacitive type touch detection means and a detection method for applying an alternating driving voltage to one side of a sensing equivalent capacitor formed between a sensing pad and a non-sensing pad and detecting a difference in voltage generated from a touch detector depending on a touch to acquire a touch signal.
Discussion of the Background
Generally, a touch screen panel is attached on display devices such as a liquid crystal display (LCD), a plasma display panel (PDP), and an organic light emitting diode (OLED), an active matrix organic light emitting diode (AMOLED) and is one of the input devices which generate signals corresponding to positions where objects such as a finger and a pen are touched. The touch screen panel has been used in wide applications such as small portable terminals, industrial terminals, digital information devices (DID), etc.
Typically, various types of touch screen panels have been disclosed. However, a resistive type touch screen panel having simple manufacturing process and low manufacturing costs has been most widely used. However, since the resistive type touch screen panel has low transmittivity and is applied with a considerable pressure, the resistive type touch screen panel is inconvenient to use, has a difficulty in implementing a multi touch and a gesture cognition, leads to a detection error, etc.
On the other hand, a capacitive type touch screen panel may have high transmittivity, cognize a soft touch, and implement better multi touch and gesture cognition, and as a result has gradually expanded its market share.
FIG. 1 illustrates an example of the existing capacitive type touch screen panel. Referring to FIG. 1, transparent conductive layers are formed on upper and lower surfaces of a transparent substrate 2 made of plastic, glass, etc., and voltage applying metal electrodes 4 are formed at four corners of the transparent substrate 2, respectively. The transparent conductive layer is made of transparent metals such as indium tin oxide (ITO) and antimony tin oxide (ATO). Further, the metal electrodes 4 formed at four corners of the transparent conductive layer are formed by being printed with conductive metal having low resistivity such as silver Ag. A resistance network is formed around the metal electrodes 4. The resistance network is formed in a linearization pattern to equally send out a control signal to the whole surface of the transparent conductive layer. Further, an upper portion of the transparent conductive layer including the metal electrode 4 is coated with a passivation layer.
In the capacitive type touch screen panel as described above, a high-frequency alternating voltage is applied to the metal electrode 4 and thus is applied over the whole surface of the transparent substrate 2. In this case, when the transparent conductive layer on an upper surface of the transparent substrate 2 is lightly touched with a finger 8 or a conductive touch input means, a change in current is sensed by a current sensor embedded in a controller 6 while a predetermined amount of current is absorbed into a body and current amounts at each of the four metal electrodes 4 are calculated, thereby cognizing touched points.
However, the capacitive type touch screen panel as illustrated in FIG. 1 is based on a method for detecting a magnitude of micro current. As a result, the capacitive type touch screen panel needs an expensive detection apparatus and therefore a price of the capacitive type touch screen panel goes up as well as the capacitive type touch screen panel is hard to implement a multi touch for cognizing a plurality of touches.
To overcome the above problems, the capacitive type touch screen panel as illustrated in FIG. 2 has been mainly used in recent years. The touch screen panel of FIG. 2 is configured to include a lateral linear touch detection sensor 5a, a longitudinal linear touch detection sensor 5b, and a touch drive IC 7 analyzing a touch signal. The touch screen panel is based on a method for detecting a magnitude of capacitance formed between the linear touch detection sensor 5 and the finger 8 (FIG. 1) and scans the lateral linear touch detection sensor 5a and the longitudinal linear touch detection sensor 5b to detect a signal, thereby cognizing the plurality of touched points.
However, when the touch screen panel as described above is installed on a display device such as an LCD, the touch screen panel is hard to detect the signal due to noise. For example, the LCD uses a common electrode. In some cases, an alternating common voltage Vcom is applied to the common electrode. Further, the common voltage Vcom of the common electrode acts as noise at the time of detecting the touched point.
FIG. 3 illustrates an embodiment in which the existing capacitive type touch screen panel is installed on the LCD. A display device 200 has a structure in which a liquid crystal is sealed between a TFT substrate 205 and a color filter 215 disposed thereover to form a liquid crystal layer 210. To seal the liquid crystal, outer portions of the TFT substrate 205 and the color filter 215 are bonded to each other by a sealant 230. Although not illustrated, polarizing plates are attached to upper and lower portions of a liquid crystal panel and back light units (BLUs) are additionally installed thereto.
As illustrated, the touch screen panel is installed on the display device 200. The touch screen panel has a structure in which the linear touch detection sensor 5 is put on the substrate 1. A protection panel 3 for protecting the linear touch detection sensor 5 is attached on the substrate 1. The touch screen panel is bonded to an edge portion of the display device 200 by an adhesive member 9 such as a double adhesive tape (DAT) and forms an air-gap 9a between the adhesive member 9 and the display device 200.
In this configuration, when a touch is generated as illustrated in FIG. 3, a capacitance such as Ct is formed between the finger 8 and the linear touch detection sensor 5. However, as illustrated, a capacitance such as common electrode capacitance Cvcom is formed between the linear touch detection sensor 5 and a common electrode 220 formed on a lower surface of the color filter 215 of the display device 200 and an unknown parasitic capacitance Cp is also applied to the linear touch detection sensor 5 due to a capacitance coupling between patterns, manufacturing process factors, etc. Therefore, a circuit like an equivalent circuit of FIG. 4 is configured.
Here, the existing touch screen panel detects a variation of Ct which is a touch capacitance to cognize a touch and components such as Cvcom and Cp act as noise in detecting the Ct. In particular, the Cp by the capacitance coupling between the patterns is ten times as large as the Ct which is the touch capacitance, and therefore touch sensitivity may be degraded due to the Cp.